定义：是一种微观结构，可以在三个维度上限制载流子。

量子点是一个非常小的结构，例如一个纳米晶体嵌入到另一个半导体材料中，可以在三个维度上限制电子或其他载流子。 
载流子限制是一种量子效应。它可以完全改变受限制粒子的态密度。对于理想隔离度的量子点来说，它具有分离的能级，对应的是δ形状的态密度且在δ峰值之间没有量子态。这一行为在原子中很常见，因此，在这一角度可将量子点看做一种人造原子，其能级可以通过改变结构来进行调制，例如，通过控制量子点的尺寸或者材料组分。实际中，常常采用大量的量子点，并且它们的尺寸分布会在一定程度上改变态密度，即引起非各向同性展宽。 
可以采用半导体材料制作量子点。有时薄的量子阱是采用分子束外延（Molecular Beam Epitaxy, MBE）或者金属有机化学气相沉积（Metal-Organic Chemical Vapor Deposition, MOCVD），其厚度可能存在一些涨落。在特定条件下，量子点可以以自组织的方式生长，这样它们可以得到更加一致的尺寸和分布。然后它们就在衬底材料上快速生长。通常金字塔形状的量子点的尺寸在5-20nm；因此，量子点可以看做纳米技术中的一种。它们的密度可达单位平方分米109 个量子点的量级。大多数情况下，一个器件需要同时使用很多的量子点，然而有些量子光学实验只需要单个量子点。 
量子点的溶液制备也需要采用一些技术。其中，一些原始的化合物在高温下溶解在有机溶剂中。化合物逐渐转化成单体，后者在溶液中变得过饱和，然后纳米晶体逐渐成核继续生长。得到的胶体溶液可以用来制备层状结构，包含很高密度的量子点。胶体悬浮量子点的主要优势在于成本非常低的制备大量的量子点。这种方法在发光二极管中非常有优势，但是其它应用中也可以采用，例如在投影仪中，其中电激发的量子点可提供像素点的辐射光，无须采用背景发光。 
若在图形衬底上生长，则可以控制量子点的位置和大小。 

应用 
量子点可应用在很多应用中： 

• 量子点最早的应用是在彩色玻璃上形成漂亮的颜色，例如在教堂的玻璃上。 
• 量子点可以实现制备的激光二极管具有很低的阈值泵浦功率和低温度灵敏度。 
• 量子点可用在白光发光二极管（LED）中：它们由蓝光或者近紫外光LED激发，然后辐射绿光和红光（类似于磷的作用），整体得到的是白光。 
• 在半导体饱和吸收反射镜中（SESAM），量子点作为吸收器，具有很低的饱和影响。这种量子点吸收器可以包含在玻璃基体中。 
• 量子点可看做高灵敏光电探测器的一部分，并且以后还可以在高效太阳能电池中发挥作用。 
• 在量子编码中，量子点可用作单光子发射器。 
• 量子点还可以用在量子计算中。 
• 提到的功能还可以在量子纳米光子学中实现。 

目前技术上最重要的应用就是发光二极管和激光二极管中。量子点半导体激光器也有望替代一些目前正在用的量子阱激光二极管。

Definition: microscopic structures confining charge carriers in three dimensions

A quantum dot is a nanoscale structure, e.g. a semiconductor nanocrystal which can confine electrons or other carriers in all three dimensions. It is usually embedded in another semiconductor material or in a glass, but there are also colloidal quantum dots in a liquid (a colloidal suspension). A quantum dot must have a band gap energy which is smaller than that of the surrounding medium, because otherwise the excitation energy could easily be lost in the surroundings.

The carrier confinement is a quantum effect. It totally changes the density of states for the confined particles, compared with the density of states for a larger piece of the material. For an ideal isolated quantum dot, there are discrete energy levels, corresponding to a delta-shaped density of states with no states in between the delta peaks. Such a behavior is known from atoms; in this sense, quantum dots can be considered as a kind of artificial atoms where the energy levels can be adjusted by design, e.g. by controlling the quantum dot dimensions or the material composition. In reality, large ensembles of quantum dots are normally used, and their size distribution leads to a somewhat smeared-out density of states, i.e. to inhomogeneous broadening.

Quantum dots can be fabricated from semiconductors. This can even accidentally happen when thin quantum wells are fabricated with molecular beam epitaxy (MBE) or metal–organic chemical vapor deposition (MOCVD), where some fluctuations of the thickness can occur. Under certain conditions (Stranski–Krastanov growth of a lattice-mismatched material on some substrate, e.g. InAs on GaAs), quantum dots can be grown in a self-organized fashion, so that they acquire more consistent sizes and distribution. Subsequently, they are often overgrown with the substrate material. Typical dimensions of the often pyramidally shaped quantum dots are of the order of 5–20 nm; quantum dots are therefore considered to be a topic of nanotechnology. Their density on a surface can be of the order of 10⁹ dots per square centimeter. In most cases, a large number of dots are simultaneously used in a device, although some quantum optics experiments require single quantum dots.

There are also techniques for solution processing of quantum dots. Here, some precursor compounds are dissolved in an organic solvent at high temperature. When the precursor is increasingly converted to monomers, the latter may become supersaturated in the solvent, so that nanocrystals start to nucleate and grow further. The resulting colloidal solution can then be used to fabricate a layer containing a substantial density of quantum dots. The main attraction of colloidally suspended quantum dots is the prospect of fabricating them cheaply in large amounts. This would be attractive e.g. for large light-emitting diodes, but other applications are also envisaged, e.g. in displays [8], where electrically excited quantum dots would provide the light emission of the pixels, removing the need for background illumination.

Position and size control of quantum dots is also possible by growth on patterned substrates.

Applications

Quantum dots are useful for a variety of applications:

• The perhaps oldest application of quantum dots is the formation of beautiful colors in stained glasses, e.g. in church windows.
• Quantum dots make possible the fabrication of laser diodes with very low threshold pump power and/or low temperature sensitivity.
• Quantum dots can be used in white light-emitting diodes (LEDs): they are excited with a blue or near-ultraviolet LED and emit e.g. red and green light (acting as a kind of phosphor), so that overall a white color tone is achieved.
• In semiconductor saturable absorber mirrors (SESAMs), quantum dots can serve as absorbers with a very low saturation fluence. Such quantum dot absorbers can also be contained in a glass matrix.
• Quantum dots can be parts of very sensitive photodetectors, and in the future they may function in efficient photovoltaic cells.
• In the context of quantum cryptography, quantum dots can serve as single-photon emitters.
• Quantum dots might also be suitable for performing quantum computations.
• The mentioned functions can also be realized in the context of quantum nanophotonics.

The so far technologically most important applications are probably those in LEDs and laser diodes. Quantum dot semiconductor lasers are expected to replace some more of the currently used quantum well laser diodes.

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